In general, combustion apparatuses are disposed in heating apparatuses in which water is heated by using combustion heat generated while fuel is burnt, and the heated water circulates along a tube to provide heating an indoor space or hot water.
Referring to FIG. 1, a general combustion apparatus according to a related art includes a blower 10 supplying air, a gas supply part 20 for supplying a combustion gas by adjustment of a valve 22 through a gas supply tube 21 connected to one side of the blower 10, a burner 20 for burning a mixed-gas in which the air is mixed with the gas, a combustion chamber 40 in which the mixed-gas is burnt by ignition of the burner 30, a heat exchanger 50 for heating water supplied through a heating water supply tube 62 after being introduced through a heating water return tube 61 to circulate in the combustion apparatus, by using the combustion heat of the combustion chamber 40, and a duct 70 through which an exhaust gas passing through the heat exchanger 50 is discharged.
In this combustion apparatus, a turn-down ratio (TDR) of the burner is set. The TDR represents ‘a ratio of the minimum gas consumption to the maximum gas consumption’ in a gas combustion apparatus in which the gas is variously adjusted in amount. For example, when the maximum gas consumption is 30,000 kcal/h, and the minimum gas consumption is 6,000 kcal/h, the TDR may be 5:1. The TDR may be limited according to whether how low the minimum gas consumption for maintaining stable flames can be adjusted.
The gas combustion apparatus gradually increases in convenience when using the heating and hot water as the TDR increases. That is, although the combustion is performed with the maximum flames in the beginning of the combustion in order to reach a desired heating temperature as soon as possible, when the combustion temperature reaches near the desired heating temperature, a gas amount supplied to the burner gradually decreases to perform the combustion. In this case, since the minimum gas consumption is high, if the TDR is low, it may be difficult to reduce and control the gas amount in order to reduce an output of the burner.
In particular, when the burner operates in an area where loads of the heating and hot water are low, the combustion apparatus may be frequently turned on and off to allow a combustion state to be unstable, thereby increasing deviation at the time of temperature control and deteriorating durability of the device. Thus, methods for improving the TDR of the burner applied to the combustion apparatus have been suggested.
As a prior art related to the methods for improving the TDR, there is a combustion apparatus of a gas boiler, the combustion apparatus including a blower for supplying air needed for combustion, a proportional control valve for adjusting a supply flow rate of a gas, a nozzle part connected to the proportional control valve to supply the gas by opening/closing of an auxiliary valve and in which a plurality of nozzles are parallelly connected to each other, a mixing chamber for mixing the air supplied from the blower with the gas passing through the nozzle part to supply the mixed-gas to a burner surface, and a control part for controlling RPM of the blower to supply a flow rate of the air only needed for the combustion according to opening/closing of the proportional control valve and the auxiliary valve, which is disclosed in Korean Patent Registration No. 10-0805630.
According to the above-described structure, the nozzle part to which the gas is supplied may be parallelly disposed in multi-stages, and opening/closing of each of the nozzle part may be controlled to correspond to an output of the burner, to improve the TDR, thereby increasing combustion stability on a low output area.
However, in the combustion apparatus according to the related art, the combustion gas such as nitrogen oxide (NOx), carbon monoxide (CO), and so on, generated at a high flame temperature may be discharged as it is into the atmosphere through the duct via the heat exchanger. Thus, the combustion apparatus may be harmful to the environment and reduced in lifespan of components thereof.